The diagnosis of pathological or other conditions in human beings and animals is often carried out using immunological principles. These principles are used for the detection of antibodies or antigens in the body fluids of the living beings. An antigen is a foreign substance which, when it is applied to the living being, brings about the formation of certain substances which are soluble and known as the antibody. Any substance such as, for example, a protein, which is normally not present in a specific living being, can cause the formation of antibodies when it is applied to the living being under suitable conditions.
After their formation, the antibodies react with the antigens and in this way protect against infections in the case of a bacteria or virus foreign body.
Immunological test processes depend on the antigen-antibody reaction, which usually manifests itself by insolubility or agglutination.
In general, the presence of an antigen or an antibody is confirmed or determined by adding the corresponding antibody or the corresponding antigen to a body fluid of the living being, mainly urine, blood serum or a specially treated blood extract. However, other body fluids can also be used. The presence or the absence of the antibody or the antigen in the body fluid of the living being is ascertained by establishing the occurrence or nonoccurrence of an antigen-antibody reaction.
Because some complexes only form very slowly and have very small particle sizes, it is necessary to use carriers in order to make them visible. In a hitherto preferred method the antibody or the antigen was bound by means of a carbodiimide via an amide bond to discrete particles of carboxylated latex polymers such as, for example, carboxylated copolymers of butadiene and sytrene.
This method has, however, the disadvantage that during the coupling of the protein (antibody or antigen) to the latex particles, there occurs as the side-reaction, because of the use of carbodiimides, an undesirable lattice-like polymerisation of the protein used and, accordingly, a part of the often very expensive protein is lost for the coupling with the carrier.